The presence/absence data of Nymphaea alba L., Nuphar lutea (L.) Sm. and Nymphoides peltata (Gmel.) O. Kuntze in 588 water bodies throughout The Netherlands were converted into logistic response curves with respect to alkalinity. For Nuphar lutea and Nymphoides peltata maximum probability of occurrence was found at 2.86 and 3.76 meq l−1, respectively. Nymphaea alba has a broad ecological amplitude with respect to alkalinity in comparison with Nuphar lutea and Nymphoides peltata. Within the 95% confidence interval no optimum for Nymphaea could be determined. Uptake capacity for dissolved inorganic carbon (DIC) was examined using the pH-drift technique. In a 1-mM NaHCO3 solution the DIC-extracting capacities of Nymphaea alba, Nuphar lutea and Nymphoides peltata were compared with those of the HCO3−-using macrophyte Potamogeton gramineus L. Unlike the situation for Potamogeton gramineus, no uptake of HCO3− could be registered by the floating and submerged laminae of the 3 nymphaeid species studied. A very limited uptake of HCO3− was measured when Nymphaea alba, Nuphar lutea and Nymphoides peltata seedlings were cultivated in solutions with a high bicarbonate concentration. Under natural conditions uptake of HCO3− can be neglected.
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